1. Field of the Invention
The present invention relates to a CMOS image sensor and fabricating method thereof. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for enhancing photo-response characteristics and protecting a microlens in packaging by embedding the microlens in a passivation layer pattern.
2. Discussion of the Related Art
An image sensor is a semiconductor device that converts an optical image to an electric signal. Image sensors can be classified into charge coupled devices (CCD) and CMOS (complementary metal oxide silicon) image sensors. In a CCD image sensor, a plurality of MOS (metal-oxide-metal) capacitors are arranged close to one another to transfer and store electric charge carriers. In a CMOS (complementary MOS) image sensor, a plurality of MOS transistors corresponding to the number of pixels are fabricated by CMOS technology using a control circuit and a signal processing circuit as peripheral circuits. A switching system of sequentially detecting outputs using the MOS transistors is also adopted.
Microlenses of the related art CMOS image sensor are formed on a passivation layer; thus, the microlenses are vulnerable to packaging. Hence, photo-response characteristics of the CMOS image sensor are degraded and overall process throughput is lowered.
A CMOS image sensor and fabricating method thereof according to a related art are explained with reference to the attached drawing as follows.
FIG. 1 is a cross-sectional diagram of a CMOS image sensor according to a related art.
Referring to FIG. 1, a photodiode 11 is formed on a semiconductor substrate 10. A first insulating layer 12 is formed on the semiconductor substrate 10 including the photodiode 11. A via hole 13 is formed by selectively etching the first insulating layer 12. A metal layer is deposited on the first insulating layer 12 including the via hole 13 and is then patterned to form a metal line 16 in a pixel area 14 and a pad 17 in a peripheral area 15. A second insulating layer 18 is formed of a material for interlayer insulation, such as oxide, etc., on the first insulating layer 12 including the metal line 16 and the pad 17. The second insulating layer 18 is then planarized.
A passivation insulating layer 19 may be formed of nitride. The passivation insulating layer 19 is planarized by CMP (chemical mechanical polishing) and is then selectively etched to form an opening 21 on the pad 17. A microlens material layer (not shown) is formed on the passivation insulating layer 19. A photoresist layer (not shown) is coated on the microlens material layer. The photoresist layer is patterned to form a photoresist pattern (not shown). The microlens material layer is selectively etched to form a microlens material layer pattern (not shown) using the photoresist pattern as a mask. Reflowing is carried out on the microlens material layer pattern by baking to form a spherical microlens 20.
However, the related art CMOS image sensor and fabricating method thereof have disadvantages. Since the microlens is formed on the passivation layer, the microlens can be damaged in subsequent packaging. Hence, a photo-response characteristic of a device is degraded and process throughput is lowered.